Something like this:

Advantages of 3-phase include reducing the number of wires needed whilst helping to balance the load.   Domestic customers are typically supplied single-phase from a delta/wye transformer, with the delta connected to 3-wire 3-phase, no earth or neutral.   The wye side, has neutral centre-point, which is also earthed.   Typically homes are wired single-phase in balanced groups to one of the three phases, plus an actual neutral wire running back to the transformer, and maybe an actual earth wire as well.  The neutral actively balances the system.

Out in the sticks, it’s common to find farms and small groups of houses some distance from the transformer.  Feeding them standard domestic single-phase 240V in the same way as local homes wastes wire whilst voltage drop causes poor regulation.  An alternative is to connect distant customers with only two wires across two phases, resulting in a single-phase high voltage with better regulation that needs less copper.  However, at the remote end another single-phase transformer is needed to step-down to domestic single-phase volts. One side of this transformer is earthed, and this also provides neutral.   Not the same load-balancing neutral provided by the wye transformer, but it works well enough for the consumer!  Not unusual for a hamlet to grow big enough for this system to become unsatisfactory, in which case proper 3 phase and with a delta/wye substation will replace it.

As there are other distribution schemes, I hope the experts won’t shoot me for not explaining their favourite!  (Looks like Noel’s village has one, where the ‘step down’ transformer is centre-tapped to provide two domestic single-phase outputs.)

Dave

Hi, typical rural pole supplies these days are at 11KV (between phases). A 3 phase line is normally run out from the 33/11KV substation. This splits down to a 2 wire system further out. These wires are delta connected and do not have a neutral.

The local pole mounted transformer steps this down to 240V of which one side of the supply (call it neutral ) is grounded at the pole as well as in the consumers premises. For a high load situation the transformer may be wound for 240/0/240, so giving 240v and 480v supplies

The ungrounded 11KV supply will continue to operate if a tree or something hits one of the lines, an advantage in rural areas.

In urban areas there is a similar situation but the substation is normally supplied with 3 phase 11KV, again delta connected. The local transformer steps this down to 440v 3 phase, which is fed along the underground cable and topped off single phase 240v for each house, with a 3 phase supply for small businesses. A neutral is provided by an earth plate at the substation to whish the cable sheath is often connected.

As 3 phase is a balanced system and the currents can cancel, the neutral core in the street cable is often of smaller cross section,

The 11KV distribution system is fed from a 33KV system, again delta connected.

Higher system voltages are 66KV, 132KV, 275KV amd 400KV. These are bulk transmission voltages and are neutral connected, often using auto type transformers to reference the system to earth and reduce insulation stress.

This is a rough description of the UK system, other countries vary and in Australia the SWER (single wire, earth return) is used in some remote areas to save costs

Hope this helps, Ed

I will leave the reader to work out why 2 phase is 240/480V and 3 phase is 240/440 !!!

It’s actually +10% to -6% of 230v. Nothing to do with companies being cunning. It comes from when the nominal supply voltage was harmonised in Europe. Different countries had slightly different declared voltages. The electricity supply system in the UK was not changed so transformers did not have to be changed.

I stand corrected. It was done like that so the suppliers didn’t have to actually do anything. i.e. just shuffle the numbers.

Bob